Dimensionless quantity calculated as the ratio of momentum diffusivity (kinematic viscosity)
\nu to thermal diffusivity
a:
| (1) | {\rm Pr} = \frac{\nu}{a} |
For most gases over a wide range of temperature and pressure, Prandtl number is approximately constant at around
{\rm Pr} = 0.71.
For water {\rm Pr} = 7.56.